Limp Mode Problem - PLEASE HELP

[bronco2v8]

I have a 96 Prelude with the H23A1, OBD1 ECU with conversion harness & I've been battling this strange running issue for quite awhile now & I just can not figure it out!!

Please watch this video to hear what it's doing.
http://youtu.be/XJse0SPER3k
The car starts out fine, then it does it's hiccup briefly at 1:50, but then clears up until about 5:20 when it just won't come out of it. Listen to it for about a minute, you'll hear what my problem is & then how it clears up again, starts going, then does it again. So very frustrating!!

It has a mind of it's own & decides to hit limp mode at random times & comes out of it whenever it feels like it. Holding the throttle down makes it worse, sometimes up-shifting to 4th will make it snap out of it, but not always. Most of the time you have to put it into neutral & return it to an idle then it will behave for a little while before it starts acting up again.

PLEASE, if anyone has a clue why my car keeps doing this I'd really appreciate it if you share your knowledge. I am going out of my mind trying to figure this problem.

I have replaced these things....
3 ECU (2 manuals, 1 automatic)
3 Distributors (1new, 1used OBD1, 1used OBD2)
1 new Crank Sensor for OBD2 distributor
2 new TPS
2 new Coolant Temp Sensors
4 IACV (all used but tested good)
2 new Ignitors
2 new Map Sensors (OBD2 mounted on top of throttle body)
3 sets of Fuel Injectors (used but all tested good)
2 Injector Resistor Boxes (used but all tested good)
2 new Knock Sensors
4 new Oxygen Sensors
2 new of each cap, rotor, pcv, fuel filter, plugs & wires

I have checked or done these things....
All grounds checked, checked, checked, plus many more added
Entire wiring harness removed, deloomed & all wires checked
Replaced all worn out electrical plugs & damaged wires
Fuel pressure is set to 45psi w/o vacuum hose
Fast idle valve plastic screw has been tightened & checked
Balance shaft eliminator kit installed
Timing belt is dead on, checked many, many times
Always use 92 octane gas
Valve lash has been checked & set many, many times
Motor has 180 compression & leak down tests show 3% leakage

I have removed these components.....
Stock dash & gauges
Vehicle speed sensor
Intake control solenoid valve
Starting air valve
Intake air bypass valve
Intake air bypass control solenoid valve
EVAP
EGR
Power Steering
A/C
Cat Converter
Everything inside the car except the main fuse panel, main relay, ABS computer & relays, radiator fan control box & the ecu.

 

[Zenmervolt]

Honestly, this is not a simple thing for an internet forum to figure out, because your car is heavily modified and therefore has about a million more variables than a normal, street-driven car.

All I can really say is that it sounds as though it's hitting the rev limiter (that is, it sounds as though you're losing spark). Have you looked at your ignition coil, plugs, and wires?

ZV

 

[bronco2v8]

Yes it is very hard to diagnose & there is another Prelude just like mine that races with me & his car does exactly the same thing as mine, almost at the same time on the track even, but his is completely bone stock.
I have a new MSD coil, new 10.2mm spark plug wires & 4 new NGK Laser Platinum spark plugs.
One of the engine sensors is causing the problem, but I just can't seem to isolate which one because the problem is so intermittent & only does it on the race track.

 

[Zenmervolt]

I have a new MSD coil, new 10.2mm spark plug wires & 4 new NGK Laser Platinum spark plugs.

Why on earth are you running platinum plugs in a race car? They are worse for performance than old-fashioned copper plugs and the only reason manufacturers fit them in new cars is because they last longer (100,000 miles vs. 15,000 to 30,000 miles). Plus, under high-temp situations (racing) platinum plugs can melt. You should definitely not be using platinum plugs for a racing engine. Go back to plain old copper.

That said, if a coil overheats, it can cause the spark to cut out or get weaker. That's why I suggested a coil. The sound suggests that you're losing spark. Have you shut the car down immediately when it's doing this and pulled the spark plugs to see what they look like (i.e. are they wet with fuel when this happens)?

ZV

 

[phucheneh]

Holy freaking shotgun repair. You've replaced so much stuff that just has nothing to do with what is happening there.

It does sound like you're hitting a rev limiter. What RPM is that occurring at? Can you watch the tach bounce off a certain point, or is it totally random?

You're running a factory PCM? Does it store any DTC's?

 

[silicon]

I have a 96 Prelude with the H23A1, OBD1 ECU with conversion harness & I've been battling this strange running issue for quite awhile now & I just can not figure it out!!

Please watch this video to hear what it's doing.
http://youtu.be/XJse0SPER3k
The car starts out fine, then it does it's hiccup briefly at 1:50, but then clears up until about 5:20 when it just won't come out of it. Listen to it for about a minute, you'll hear what my problem is & then how it clears up again, starts going, then does it again. So very frustrating!!

It has a mind of it's own & decides to hit limp mode at random times & comes out of it whenever it feels like it. Holding the throttle down makes it worse, sometimes up-shifting to 4th will make it snap out of it, but not always. Most of the time you have to put it into neutral & return it to an idle then it will behave for a little while before it starts acting up again.

PLEASE, if anyone has a clue why my car keeps doing this I'd really appreciate it if you share your knowledge. I am going out of my mind trying to figure this problem.

I have replaced these things....
3 ECU (2 manuals, 1 automatic)
3 Distributors (1new, 1used OBD1, 1used OBD2)
1 new Crank Sensor for OBD2 distributor
2 new TPS
2 new Coolant Temp Sensors
4 IACV (all used but tested good)
2 new Ignitors
2 new Map Sensors (OBD2 mounted on top of throttle body)
3 sets of Fuel Injectors (used but all tested good)
2 Injector Resistor Boxes (used but all tested good)
2 new Knock Sensors
4 new Oxygen Sensors
2 new of each cap, rotor, pcv, fuel filter, plugs & wires

I have checked or done these things....
All grounds checked, checked, checked, plus many more added
Entire wiring harness removed, deloomed & all wires checked
Replaced all worn out electrical plugs & damaged wires
Fuel pressure is set to 45psi w/o vacuum hose
Fast idle valve plastic screw has been tightened & checked
Balance shaft eliminator kit installed
Timing belt is dead on, checked many, many times
Always use 92 octane gas
Valve lash has been checked & set many, many times
Motor has 180 compression & leak down tests show 3% leakage

I have removed these components.....
Stock dash & gauges
Vehicle speed sensor
Intake control solenoid valve
Starting air valve
Intake air bypass valve
Intake air bypass control solenoid valve
EVAP
EGR
Power Steering
A/C
Cat Converter
Everything inside the car except the main fuse panel, main relay, ABS computer & relays, radiator fan control box & the ecu.

did you ever get a code set in the computer. If you had you probably would have mentioned it. Perhaps you need to see in real time what is being sent to the computer so that any condition, lean out etc, can be seen. Your car is heavily modified and those parts or any one of them could be defective somehow.

 

[bronco2v8]

Ok, so I changed the plugs to standard NGK's & replaced the coil & the car still does the same thing.
It never sets a code.
RPM's limit out to 3300.
It does it with a stock P14 ecu, both OBD1 & OBD2 & also I borrowed a chipped OBD1 ecu & it does it to.
Tried watching the scanner to see what the sensors are doing & that was no help. When it goes into limp mode all the sensors geek out & give erratic readings. Didn't see anything wrong before it hit limp mode.
I do know that the hotter the engine is the more often it does it.
I've burped & bleed the cooling system over & over & there is no air in it, but it still goes into that limp mode.
Temp is around 180 when it goes into limp mode.
Like I said before, even though my car is heavily modified, there is another identical car that races with me & his TOTALLY stock car does EXACTLY the same thing as mine at almost exactly the same time. So whatever the problem is it has to be one of the stock sensors, cause that's the only thing our 2 cars have in common. The other guy is going nuts trying to figure out the problem also.
Could it be the O2 sensor or the air temp sensor?

 

[slag]

did you ever get a code set in the computer. If you had you probably would have mentioned it. Perhaps you need to see in real time what is being sent to the computer so that any condition, lean out etc, can be seen. Your car is heavily modified and those parts or any one of them could be defective somehow.

Didn't you read the list of things he removed? He threw the computer out first thing!

 

[uclabachelor]

Have you tried replacing the car?

 

[Mark R]

I think you're going to need to get a high end scan tool/digital store oscilloscope/logic analyser with multiple analog/oscilloscope inputs and a data memory.

My next step would be to get an interposer loom made to go between the ECU and the main wiring harness, which would allow the logic analyser to be spliced in. You would then need to monitor injector lines/coil drive lines/sensor lines until you find what is going crazy during one of these attacks.

 

[Zenmervolt]

So whatever the problem is it has to be one of the stock sensors, cause that's the only thing our 2 cars have in common.

This is faulty reasoning.

Unless your ECU has been reprogrammed (which you do not indicate at all), it's very likely that the issue is something in the ECU itself that is designed to protect the stock engine.

For an engine as heavily modified as yours, you should be running a custom ECU, like a MegaSquirt. Expecting a stock ECU to appropriately handle things when you've done all kinds of odd, one-off modifications and removed multiple sensors is just ridiculous.

I think the answer here is to move to a custom EFI system and stop trying to rely on the stock ECU.

ZV

 

[phucheneh]

OP, I'm not sure who led you to believe that that is a 'limp mode'...it's not.

It doesn't even sound like the engine is actually experiencing an issue. Sounds more like your clutch is slipping...

This happens when the car is hot? And let me guess...in fourth or fifth gear?

 

[bronco2v8]

Let me make this very clear....
Hondata ECU = limp mode
Stock OBD1 ECU = limp mode
Stock OBD2 ECU = limp mode
Every single removed sensor put back = limp mode
My modified engine = limp mode
My friends 100% stock engine = limp mode

Stock ecu or chipped ecu MAKES NO DIFFERENCE.
Stock engine or modified engine MAKES NO DIFFERENCE.

The problem lies in the communication of the sensors between the ecu. One or more of my sensors are malfunctioning when the car gets hot. I do not fully understand how each sensor contributes to the fuel map & timing of the ecu, but I do know that there is a problem sensor(s) causing my issue.

When it's 50 degrees outside & my engine temp only rises to 150 degrees, the car will never go into the limp mode that triggers a 3300 rpm rev limit.
When it's 60 degrees out & my engine temp rises to 180 degrees, the will car will go into the limp mode triggering the 3300 rpm rev limit more often.
When it's 70 degrees out & my engine temp reaches 215 degrees, the car goes into that limp mode triggering the 3300 rpm rev limit.

That's why I ask....would a problem with the coolant temp sensor and/or air temp sensor cause the ecu to trigger a 3300 rpm rev limit?

 

[Zenmervolt]

You never said you'd had a chipped ECU until just now. Don't get pissy because we can't read your mind.

Also, Hondata ECUs are not plug and play; they require that you load the appropriate tune for your engine (the "canned" tunes available for download assume fairly standard engines) or that you build a custom tune. A simple s100 is barely adjustable at all and really isn't suitable for long term reaching use. The s200 and s300 models have built in data logging so you should just be able to check the logs to see what's happening.

If the ECU thinks the engine is overheating or that there are too many misfires it can throw it into limp mode. I think something like that is happening here and that you should be using a full custom time, not a chip designed for largely street use.

Finally, the coolant temps you describe seem wildly out of line. At 50 degrees ambient you should not be seeing only 150 degree coolant temps. That's horribly bad for the engine; way too cold. Potentially damaging actually. Similarly, at 70 degrees ambient you shouldn't be running 215 degree temps; while that's not quite into problematically high temps, it's above what you should be seeing on such cool days. I shudder to think what would happen if you raced on a 90 degree day; probably blow a head gasket.

I really, really, really don't think this is a faulty sensor. I think it's the ECU deciding that the engine is operating outside of design limits and trying to save it from blowing up.

I'm assuming that you are running an enlarged racing radiator and a 180 degree thermostat, since it would be foolish to go racing with the stock radiator but I'd still check the cooling system to make sure it's operating correctly.

ZV

 

[bronco2v8]

I don't know much about the Hondata ecu, my buddy came by with his Prelude to help me & we decided to pull his ecu to see what would happen. He told me that his program would run my motor just fine & it did, until my engine hit 5300 rpms at a temp of 185, then the same thing happened - limp mode. He didn't bring his laptop or software, so we couldn't check the ecu to see what happened.
Yes, big aluminum radiator with 2 big aftermarket fans.
Assuming that it is the ecu in my car because its so modified, then WHY does my friends identical Prelude that still has all the stock stuff, never been modified or changed or gutted do exactly the same thing as mine for the last year & a half?
He hasn't changed one thing on his car, but just like mine, it won't throw a code & runs great most of the time as long as it's not to hot outside. We'll both do about 5 laps on a 3/8th oval track & either mine or his will hit the limp mode, then the other one will usually do it the next lap. There are 6 4G Preludes, all the same H23 engines & mine & his are the only 2 doing it. Again mine is heavily modified, his is completely bone stock, both trigger exactly the same limp mode, limiting the car to 3300 rpms.
In my opinion it cannot be the ecu programing in any way, it has to be one of the few sensors that our 2 cars have in common.

 

[silicon]

Yes it is very hard to diagnose & there is another Prelude just like mine that races with me & his car does exactly the same thing as mine, almost at the same time on the track even, but his is completely bone stock.
I have a new MSD coil, new 10.2mm spark plug wires & 4 new NGK Laser Platinum spark plugs.
One of the engine sensors is causing the problem, but I just can't seem to isolate which one because the problem is so intermittent & only does it on the race track.

Have you investigated if there are any TSB's from Honda? Or a trouble shooting guide since a near stock prelude shows similar problems?

 

[JCH13]

Check your oil pressure sending unit and/or oil level sending unit.

I'm assuming that a low oil pressure issue is putting your car into limp mode. It appears to be the only sensor you haven't replaced several times, and in 'go fast, turn left' racing oil starvation can be a big problem because oil is always forced to one side of the sump.

What's your on-track oil consumption look like? Oil temperature? What type of oil are you using?

 

[boomerang]

Are you running a thermostat? Are you looking at temps on the gage or those provided to the ECM? I know it seems like your problem is temperature related based on your description but I have a hard time believing that could be the case. It just doesn't seem plausible.

JHC13 asked about oil consumption. An important question to ask. Because I'm wondering if you're overpowering the crankcase ventilation system. If you are sucking oil into the combustion chambers, the knock sensors will go insane because of the resultant detonation with the result being retarded timing until that doesn't work and then countermeasures will be implemented (limp mode).

Also, how much gas are you carrying when you go out on the track? Half full, quarter full, just enough to complete the session?

Additionally, I've got to ask what may be a dumb question but you're talking of swapping out ECM's and you're talking about using OBDI and OBDII versions. Really? I just can't imagine that the wiring is going to be compatible between those two. Same connectors? Wires running from the same cavities to the same sensors? Seems implausible. My plausibility meter really goes off the chart when you say you have used ECM's for both manual and automatic transmissions.

You're speaking of a conversion harness. What exactly does that allow for? I have an idea of what the purpose is but would you tell us exactly?

Also, you have removed a number of sensors and the VSS for certain and perhaps the EGR concern me. What in the ECU has been done to compensate for their being removed? You could probably easily fool the system into thinking an EGR is present (there may not be any feedback to the ECM for EGR operation so this may not be an issue at all) but the VSS? That's a pretty critical sensor.

For the purposes of fixing your problem, one thing you should do at this point is remove any preconceived notion of what the problem is. It's good to suspect something then eliminate it and move on but feeling that it absolutely has to be "x" can really get you chasing your tail. And truly, you've thrown enough parts at it that you've been chasing your tail.

Sorry, but I keep adding things as I think of them. You say you have never had a code set. Does the ECM have power when the car is off? Does the master switch (assuming the sanctioning body requires one) kill power to the ECM?

 

[Zenmervolt]

Assuming that it is the ecu in my car because its so modified, then WHY does my friends identical Prelude that still has all the stock stuff, never been modified or changed or gutted do exactly the same thing as mine for the last year & a half?

I didn't say that the ECU was doing it because your car is modified. I said it's doing it because it thinks something's wrong (either overheating, or too many misfires, etc.). That may or may not be related to the modifications and could easily occur in both a stock and modified car.

In my opinion it cannot be the ecu programing in any way, it has to be one of the few sensors that our 2 cars have in common.

If you're so sure you know what it is, then why are you here asking us for help?

The chances of the same sensor failing in the same way and causing exactly the same symptoms on both a heavily modified and a completely stock engine are extremely small. It's more likely that your engines are both experiencing the same underlying malfunction that is triggering the ECU to try to protect the engine.

Also, the Honda ECUs from that era do store codes. You should be able to retrieve the codes using this method: http://www.instructables.com/id/How-to-Read-Codes-From-Your-Check-Engine-Light-Fo/?ALLSTEPS

Of course, you'd have to re-install the stock gauges for that to work since it functions by making the "check engine" light blink.

ZV

 

[Zenmervolt]

Check your oil pressure sending unit and/or oil level sending unit.

I'm assuming that a low oil pressure issue is putting your car into limp mode. It appears to be the only sensor you haven't replaced several times, and in 'go fast, turn left' racing oil starvation can be a big problem because oil is always forced to one side of the sump.

What's your on-track oil consumption look like? Oil temperature? What type of oil are you using?

Come to think of it, IIRC the VTEC system depends on oil pressure and viscosity within the expected ranges to work. If the oil's not quite right there could also be VTEC malfunctions.

ZV

 

[master_shake_]

it almost sounds like the injectors are cutting out then turning back on

like having a stuck idle air controller.

 

[Mark R]

Turns out that this is exactly what Honda's limp mode does - it activates a rev limiter at 3300 rpm.

The point is that something is triggering the ECU to drop into limp mode - the only way to deal with this is to find out what is triggering limp mode. The ECU should be storing a code, but if it isn't, the only way is to monitor each input to the ECU to see what goes crazy before the ECU starts limping.

If the ECU isn't storing codes, then the first thing is to verify if it really is limp mode - if it is, the ECU should be cutting fuel and/or retarding spark. If something else strange is going on, then it could be some other kind of malfunction, which just happens to manifest in the same way.

 

[Zenmervolt]

it almost sounds like the injectors are cutting out then turning back on

like having a stuck idle air controller.

The hell?

The idle air control doesn't do a goddamn thing to the injectors. All it does is open a throttle plate bypass slightly to create the same effect as opening the throttle a little more to handle variations in engine load at idle. It can't cause the injectors to cut in and out. This suggestion is absolutely ridiculous.

ZV

 

[phucheneh]

Turns out that this is exactly what Honda's limp mode does - it activates a rev limiter at 3300 rpm.

The point is that something is triggering the ECU to drop into limp mode - the only way to deal with this is to find out what is triggering limp mode. The ECU should be storing a code, but if it isn't, the only way is to monitor each input to the ECU to see what goes crazy before the ECU starts limping.

If the ECU isn't storing codes, then the first thing is to verify if it really is limp mode - if it is, the ECU should be cutting fuel and/or retarding spark. If something else strange is going on, then it could be some other kind of malfunction, which just happens to manifest in the same way.

Good to know. I've honestly never heard of this. Perhaps because 1) mid 90's Hondas rarely come in with drivability problems (pretty damn bulletproof) and 2) most of them are autos and the owners don't typically push them past 3k RPM during normal driving.

I am highly dubious that this would not set a DTC, though. Especially with an OBD2 PCM. If the computer is seeing an input that is so out of whack that it is triggering this mode, it makes no sense that a code would not be stored. And I don't see it being on the output side. Misfires, a stuck VTEC valve, ect, should all set DTC's and cause fairly noticeable problems.

While all the OP's swapped parts are not exactly a definitive troubleshooting process, I would say the most likely thing is going to be that one of the parts that has remained the same is the problem. Which is to basically say, it's in the engine wiring harness. He needs to start recording livedata while the issue is present. I'd try monitoring everything at once. If that yields no useful info, I'm start monitoring just a few sensors at a time (typically the less that's being monitored, the faster the data will update).

 

[master_shake_]

The hell?

The idle air control doesn't do a goddamn thing to the injectors. All it does is open a throttle plate bypass slightly to create the same effect as opening the throttle a little more to handle variations in engine load at idle. It can't cause the injectors to cut in and out. This suggestion is absolutely ridiculous.

ZV

Its how the rev limiter works on a Honda. If the idle valve is stuck open then there is no idle control.

When the idle valve is stuck there is too much air going in to the intake.

So when the revs get to high the PCM cuts the injectors to drop the idle.

If you have a scan tool you can watch it happen.

Injector pulse width will drop every time the revs go up and then go up when the idle speed drops.

Same thing happens on Nissans when the the electronic throttle valve loses its calibration.